1. Field of the Invention
The present invention is an electronic ballast device for controlling the power to one or more gas discharge lamps, specifically, fluorescent lamps. It is directed to the problems of present ballasts used for fluorescent lamps which waste energy through excess heat generation and which also lack control options.
The present invention is able to power any of the conventional fluorescent lamps without modification. This includes, but is not limited to standard fluorescent lamps, HO, VHO, T8, T10, and T12 lamps ranging from a two foot standard lamp to an eight foot T12.
2. Prior Art Statement
Fluorescent lamps are used extensively throughout office buildings, schools, hospitals, industrial plants for lighting, as plant grow lights for outdoor lighting, and for many other uses. The power to these lamps are controlled by ballasts which have inherent problems. While fluorescent lamps with standard ballasts and less sophisticated electronic ballasts offer some benefits over other lighting techniques, such as lower energy use for comparable light output, these ballasts still waste energy through excessive heat generation and they lack the features available with the present invention. Standard ballasts use bulky energy wasting transformers to create a high voltage, low frequency signal to excite the lamp filaments. The present invention uses a low voltage, high frequency signal to excite the filaments. Existing ballasts require specific impedance matching to a specific lamp design. The present invention can power a wide range of lamp sizes without modification.
Using the present invention, lamps will burn cooler, last longer and produce a brighter light while using less electricity. The present invention also has a more sophisticated level of control then is available from the present state of the art. It can dim the lamps, delay power-up to improve lamp life, sense when a lamp is missing or burnt out and respond accordingly by reducing power or shutting down completely, and it can be controlled remotely or by a programmable unit.
The present invention does not require that the lamp be individually matched to the ballast design. The present design can power a standard 425 ma lamp, an 800 ma HO lamp, a 1500 ma VHO lamp a T8, a T10 or a T12 lamp without modification. Prior Art requires the impedance of each lamp to be matched to the ballast in order that lamp current be limited. The present device uses the performance characteristics of the transformer at the operating frequency (typically about 38 kHz) that allows the impedance of the lamps in combination with the reactance of the transformer windings and a slight frequency change to limit lamp current.
International Patent No. WO 83/02537 uses a much lower frequency (20 kHz). While it uses the frequency characteristics of the output transformer to dim the lamp by increasing the frequency, its steady state operation is in the frequency mid-band of the transformer. This coupled with the lower frequency (transformer reactance is proportional to frequency) means that during steady state operation, the lamp load must be matched to the ballast. Each additional lamp requires an additional output transformer. Further, this design requires an additional transformer in the timing circuit.
U.S. Pat. No. 4,853,598 discloses a higher frequency device (30 kHz), but one that operates in the frequency mid-band of the output transformer. This design dims by lowering voltage and must also be tailored to match the load of each lamp.
U.S. Pat. No. 4,998,045 discloses a device which operates in the frequency mid-band of the output transformer, and dims by varying the pulse width (duty cycle) and frequency of the timing circuit. This ballast must also be matched to the load.
U.S. Pat. No. 4,998,046 discloses a complex device with separate transformers for arc voltage and filament voltage. Additional lamps require extra transformer winding and additional ballast capacitors to match the new load.
While Prior Art is extensive, none of the patents disclose an electronic ballast which takes full advantage of the characteristics of the output transformer such that any size lamp can be powered without impedance matching by adding or changing components.